Although under much criticism during recent years because of polluting emissions, the internal combustion engine nevertheless represents one of the most significant inventions of all times, particularly in terms of its applications as a portable power source. However, the basic cycle has too often been utilized in devices which tend to waste much of the developed energy.
An electrically powered car has been proposed as an alternative to the internal combustion engine power plant per se. Historically, the improvements in gasoline-powered engines and invention of the self-starter eclipsed the future of the electrical vehicle for many years. The principal reason behind the lack of competitiveness of the electric automobile was the limitation of the batteries. A 20-gallon tank of gasoline can provide about 2.4 million BTUs; a lead storage battery weighing about the same as that of a tank of gasoline can provide only some 7,700 BTUs or about 2.25 kilowatt hours. The ratio then, of energy in a tank of gasoline to the energy in the same weight of conventional storage battery is more than 300 to 1. However, an automobile engine can convert only about 1/5 of the energy in the gasoline into driving power, while the electric motor can produce motive effort from nearly all the electricity derived by the battery. Thus, in total energy efficiency--a measure of the amount of energy it takes to move a car a mile--electricity outdistances gasoline. If operating costs per mile are considered there is virtually no comparison: at 1976 prices (and that was before the recent spate of oil price changes) an electric car using ordinary lead acid batteries could be operated for less than 1 cent/mile! The Energy Research and Development Administration (ERDA) predicts that by 1982 electric cars will be capable of cruising 200 miles or more on a single charge at 55 miles per hour. Even with this advantage, however, electric drive has traditionally suffered in performance when compared to that of an internal combustion engine.
The Hybrid engine-electric power plant has been offered as a means for transportation combining the advantages of the internal combustion engine and the electric battery. It has been proposed that a small fossil-fueled engine drive a generator on-board a vehicle which charges the batteries and drives the vehicle's wheels. If this is done, the vehicle can be powered by a relatively small internal combustion engine. In addition, the space devoted to the batteries can be reduced. This space can be filled with fuel having greater energy density. Relative to a pure electric car, a Hybrid vehicle has improved handling performance, and range; this is due to the lower curb weight and higher energy storage capacity. The engine is also relieved of some of the transient demands on its performance. Thus, the engine design can be optimized for low emissions to a greater extent than if it were the sole driving source. A review of some basic principles will dramatize the problems of ordinary spark ignition engines. These problems must be corrected if Hybrid vehicles are to be used efficiently.
The production of power by this type of engine represents a thermodynamic conversion of a portion of the heat energy developed into mechanical energy. The heat energy enters the engine laterally in the form of fuel. Mechanical energy appears as power available to the crankshaft or connecting rod. Unavailable or rejected heat is found in exhaust gasses, cooling water (or air) and mechanical or fluid friction. The conversion of fuel into useful energy takes place about as follows:
Air is brought into the cylinder and, either after, before, or during compression, depending on the cycle, fuel is introduced into the air and mixed with it. Upon ignition of this fuel, the heat developed raises the pressure of the products of combustion, or, at least, maintains the pressure during some motion of the piston. The fact that the piston has, against one face of it, a gas pressure greatly exceeding that of the other, inevitably results in the transmission of energy through the train of mechanism consisting of the moving piston, connecting rod and crankshaft. During the motion of the piston, the gasses of compression expand and are cooled somewhat. It has not been found economical to build an engine sufficiently bulky to expand the gasses until they reach ordinary atmospheric pressure, and consequently there is always considerable heat loss in the exhaust.
From the foregoing it will be understood that the efficiency and useful work performed by an internal combustion engine is largely dependent upon the particular physical structure in which the device is embodied. In addition, the ideal thermodynamic analysis of an internal combustion engine ignores the fact that there are several subsystems, each a thermodynamic cycle in itself, which support the operation of a practical internal combustion engine. Minimizing the energy transferred to or required by these supporting systems and reducing work lost by friction and other non-reversible processes--while an obvious starting point for an improved internal combustion engine--has not heretofore been pursued. Too often, practitioners skilled in the art have been tied to orthodox design concepts. One only has to consider a few of these supporting systems to illuminate the shortcomings of the current approach to engine design.
The lubrication system of an internal combustion engine is a vital and somewhat complex system. An engine operating with a flaming gas in its combustion chamber would not last too long with simple metal to metal contact between the moving parts. One of the most difficult jobs for the lubrication system is lubricating the piston within the cylinder. During a portion of the stroke, the lubricated walls of the cylinder are exposed to incandescent gasses which tend to burn off the film of lubricating oil. An elaborate cooling system is often required to adequately maintain the metal surfaces cool enough to save the lubricating film from destruction. Providing a continuous supply of relatively cool oil to the piston rings and cylinder walls requires a very involved system of internal ports and passageways within the connecting linkage joining the piston and the drive shaft. Interruption of flow through any one of these passages even for a short period of time can quickly lead to piston and cylinder deterioration. Ordinary internal combustion engines typically employ a wrist pin, a connecting rod and a crankshaft to transfer the reciprocating action of the piston to a shaft rotation. Each of these components requires lubrication and the overall assembly must be kept within a fine degree of balance. Friction resulting from poor lubrication and vibration resulting from running gear or crankshaft imbalance wastes energy and eventually leads to engine deterioration and damage. Finally, the cost of fabricating these components is quite expensive because of the internal passageways and precision alignment required. A new engine which is predicated on simplifying lubrication, cooling and balance requirements would not only be less expensive to build and to buy but also less expensive to operate and to maintain.
Since the combustion of fuel in an internal combustion engine requires time, maximum power is typically obtained by "timing" the ignition of the fuel by a sparkplug so as to distribute the combustion process before and after the top dead center position of the piston within the cylinder. Optimum spark advance depends principally upon the air-fuel mixture, the combustion chamber design, turbulence, engine speed, the number of sparkplugs, and sparkplug location. Maximum power air-fuel ratios require the minimum spark advance. For example, low speed engines require about 10 to 20 degrees of spark advance, while high speed automobile engines require 30 to 40 degrees of spark advance. Spark advance in ordinary internal combustion engines is controlled by engine speed and manifold vacuum; increases in both of these independently increase spark advance. The timing train or apparatus used to operate the intake valves and exhaust valves and the sparkplugs is ordinarily a set of mechanical linkages between the shaft of the engine and the rotational or reciprocating components operating the valves and ignition system. Eventually these "mechanical connections" come out of alignment due to deterioration of metal-to-metal contacting parts and linkages. Similarly, in the case of ignition systems using a distributor, the mechanical wearing of the "points" affects the timing of the engine. Recently, so-called "solid state" devices have been marketed that reduce the dependence upon mechanical connections between the engine drive shaft and the device firing the sparkplug. However, it is truly extraordinary for an engine not to use a "linkage" to operate its intake and exhaust valves. Again, this is a reflection of the orthodox thinking that has too often been used in the design of internal combustion engines.
The combustion of fuel in an internal combustion engine is not a continuous affair, but a series of individual explosions, each one requiring a metered amount of fuel to be individually ignited. In most spark-ignition engines, fuel is injected into either a super-charger, the intake manifold, or the combustion chamber. Fuel injection insures a more uniform distribution of fuel over that obtainable through carburetion. Super-charging is a process which increases the amount of fuel-air mixture per cycle of an engine above that of a normally aspirated (carbureted) engine. In addition, fuel injection improves the distribution of fuel and tends to suppress combustion "knock" by increasing the mixture richness. Thus, higher power outputs are obtainable with the use of less volatile fuel. Like the inlet and outlet valves, the fuel injector is ordinarily actuated by a mechanical linkage. When this "mechanical connection" comes out of adjustment, the fuel distribution becomes non-uniform and the power output deteriorates. An automobile propelled by a hybrid engine will have a limited advantage over conventional vehicles if it is dependent upon a fossil-fueled power plant requiring the same periodic engine tune-ups.
Since the combustion of fuel in an internal combustion engine is not continuous, its power is delivered cyclically and in a fashion which fluctuates widely. This power pulsation is ordinarily controlled by using an ordinary flywheel or by overlapping the power pulses through multi-cylindered drive shaft arrangements. In the same sense, a "mechanical connection" is used to set or regulate the timing between the various cylinders to stabilize the output rotation of the engine. Similarly, unless a relatively large number of cylinders is used, each cylinder tends to oppose the other cylinders at least for a portion of its cycle. Thus, in an effort to achieve a balanced shaft output, the conversion of heat energy into rotational or mechanical energy suffers. An engine design providing an output that is relatively constant between spark firings would have improved fuel efficiency.
From the foregoing it is easily understood that an engine not depending upon traditional subsystems (processes which inherently operate at reduced efficiency and require periodic maintenance and tune-up) would of necessity improve the conversion of heat energy into mechanical energy. The elimination of complex mechanical linkages and precision lubrication systems would also improve the efficiency of an internal combustion engine. Fabrication costs would also be significantly reduced. Similarly, a spark-ignition system, the timing of which is essentially independent of direct mechanical connections, would reduce the need for periodic tune-ups and at the same time improve the overall fuel efficiency and smoothness of operation of the engine.
Such an engine when combined with an advanced electric battery to propel an automobile would be a welcomed and long sought-after entry into the marketplace. A hybrid power plant of the type described would go far to eliminate polluting emissions and reduce our country's dependence on foreign oil. In the same sense such an advanced engine could be used in other applications requiring a portable source of power. Marine power plants and home energizing generators are two applications that readily come into mind. Other applications will become apparent from the detailed discussion following.